Defining Properties

Thin Film Stacks Standard Expert

TracePro uses Thin Films to calculate the specular properties of dielectric multilayer stacks. The Thin Film calculations in TracePro assume a coherent plane wave of light and follow the theory from Born & Wolf section 1.6.3 (7th expanded edition, Cambridge, 1999). Grazing incidence is not a "special case,” so the calculations are valid for all angles of incidence, provided the "coherence assumption" holds.

Thin Films work in conjuction with the Material Properties for the index and absorption coefficients, the Stack Editor to define the layers of the film and with the Surface Properties as a component of a Surface Propety. You can not directly apply a Thin Film to a surface in TracePro rather you apply a Surface Property that contains a Thin Film. The Stack Editor is shown in Figure 3.26.

If the materials are entered with wavelength and temperature dependence, the stack and subsequent surface property is fully dispersive.

Any number of layers may be used to define a Thin Film Stack. The thickness should be greater than zero but if a zero thickness is entered the layer is effectively removed from the stack during evaluation.

Using the Stack Editor

The Stack Editor provides a means to add or change the various layers to a stack. Select Define|Edit Properties|Thin Film stacks to open the Stack Editor window.

Stacks are entered like a table with the first layer, the top row, in contact with the incident medium and the last layer, the bottom row, in contact with the substrate medium. The substrate medium corresponds to the Object that the Surface Property is applied to.

TracePro stacks are constructed using the Material Properties database. Any material defined in the various material catalogs can be inserted as a layer. Each stack layer also requires a thickness (in microns).

TABLE 3.11. Fields in the Stack Editor Information and Grid Panels

Catalog	Name of property catalog selected from dropdown list.
Name	Property name selection box. Select a name in the Name dropdown list box or
	by typing the name into the Name text box. If the typed name finds a match in
	the database, its data is displayed on the spreadsheet.
Description	The description is a field for text intended to contain added information about
	the property.
Thickness	Use this column to accept or edit the physical thickness of the layer in microns.
Material	Use this column to accept or edit the name of an available catalog.
Catalog
Material Name	Use this column to accept or edit the name of a material.

Thin Film Stack Editing Note

The thin film stack is a special case because it is subordinate to surface properties. That is, after creating a stack property with the thin film stack editor, the next step is to open the surface property editor to use the stack property in a surface property. In the Surface Property Editor, set the type = stack. You can

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Thin Film Stacks

now add scatter, which is not available in the Thin Film Stack Editor. By becoming part of a surface property, the stack property is enhanced with scatter before being applied to a surface. The sequence of steps is:

1.Create the Stack Property in the Stack Property Editor.

2.Create the Surface Property in the Surface Property Editor. Set the type = Stack.

3.Apply the Surface Property to a surface in your model.

Entering a Single Layer Stack

Many lenses are coated with a single layer of Magnesium Fluoride (MgF), a common Anti-Reflection coating in the visible wavelength region. Typically this is a Quarter Wave Optical Thickness (QWOT) in the center of the visible spectrum. For maximum transmission at a given wavelength, select a physical thickness of 0.25 λ/n to achieve a Quarter Wave Optical Thickness.

FIGURE 3.26 - Stack Property Editor

To create a Thin Film Stack:

1.Select Define|Edit Property Data|Thin Film stacks to open the Stack Editor editor window.

2.Choose a catalog from the catalog dropdown list.

3.Click on Add Property, enter a name for your new property and click OK.

4.Edit the Thicness and Material for each layer in the stack. The data columns are drop down lists from which a Catalog and THEN Name are selected.

5.Press the Insert or Delete buttons to add/remove layers.

6.Select File|Save from inside the Stack Property editor window or close the Stack Property editor and answer yes to the question “property has changed, save data?” Your new property is now available in the Property Database for future use.

Note: Because the Material Property Database is used, the Stacks are fully dispersive when the Material Data contains wavelength and temperature data.

TracePro 5.0 User’s Manual

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Defining Properties

After a Thin Film Stack is defined access the Surface Property Editor by selecting

Define|Edit Property Data|Surface Property to define a Surface Property of type Stack. For more information about “Creating a new surface property”, see page 3.28.

FIGURE 3.27 - Stack Entered Into Surface Property Editor

When the AR Surface Property is applied to an Object made from Schott BK7 glass, we see a reflectance of less than 4% in the visible wavelength range. An uncoated piece of BK7 has a reflectance of just over 4%. See Figure 3.28 on page 3.45. The plot is viewed by opening the Plot Tab in the Surface Property Editor and setting the Plot Options for an Incident Medium of Air and a Substrate of Shott BK7 glass. For more information about “Surface Property Plot Tab ”, see page 3.29.

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